By looking vertically down, its
angular or lateral movements could be measured with accuracy. Between noon
and 4.15 P.M. the pinna changed its position to one side by only 7o; but
not continuously in the same direction, as it moved four times to one side,
and three times to the opposite side,
[page 377]
in one instance to the extent of 16o. This pinna, therefore circumnutated.
Later in the evening the four pinnae approach each other, and the one which
was observed moved inwards 59o between noon and 6.45 P.M. Ten observations
were made in the course of 2 h. 20 m. (at average intervals of 14 m.),
between 4.25 and 6.45 P.M.; and there was now, when the leaf was going to
sleep, no swaying from side to side, but a steady inward movement. Here
therefore there is in the evening the same conversion of a circumnutating
into a steady movement in one direction, as in the case of the main
petiole.
It has also been stated that each separate leaflet circumnutates. A pinna
was cemented with shellac on the summit of a little stick driven firmly
into the ground, immediately beneath a pair of leaflets, to the midribs of
both of which excessively fine glass filaments were attached.
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